JP2012079460A - Lighting unit using concealment lens sheet and display device equipped with this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conceal an image of an optical structure provided on a reflection surface of a light guide body and improve luminance in a frontward direction as well.SOLUTION: The lighting unit 3 is provided with a light source 8, a light guide plate 9 with an optical structure mounted on a reflection surface 14, and a concealment lens sheet 10. The concealment lens sheet 10 has a first linear lens 18 of an almost convex-curve-shaped cross-section arrayed on a base material 17. When a displacement of the linear lens 18 toward the array direction from a point where the linear lens 18 contact with the base material is x, a refractive index is n, an angle made by a vertical direction to the incident surface and the incident light is θ, an upper frame line of the first linear lens is f(x), an inclination of tangent of the upper frame line f(x) is φ(x), a light-distribution distribution of the first linear lens to the array direction is g(θ), a negative correlation exists between an inclination density distribution D(ξ) as expressed by a formula (2) using the angle(ξ) as shown by a formula (1) and the light-distribution distribution g(θ).

Description

  The present invention relates to an illumination unit mainly used for illumination optical path control and a display device including the illumination unit.

  A flat panel display typified by a liquid crystal display device (LCD) is widely used in which a lighting device necessary for recognizing provided information is incorporated. The power consumed by this lighting device occupies a considerable portion of the power consumed by the entire liquid crystal display device. Therefore, reducing the power consumption of the lighting device necessary to provide a predetermined luminance can contribute to power saving of the entire liquid crystal display device.

By the way, as a lighting device used for a liquid crystal display device, there are mainly a direct type and an edge light type. The direct type illumination device can be provided with a large number of light sources, and thus is applied to a large-sized (mainly 20 inches or more) liquid crystal display device. On the other hand, the edge light method is not applicable to a large display device because the arrangement position of the light source is limited, and is mainly applied to a small display device such as a notebook personal computer, a liquid crystal monitor, or a portable information terminal.
Recently, however, LED (Light Emitting Diode Light-Emitting Diode) instead of cold-cathode tubes has begun to be used as the light source for lighting devices. The device has begun to be used in medium-sized or large-sized liquid crystal display devices of 20 inches or more.

  In general, the edge light system has a structure in which a light source is disposed only on an end surface of a light-transmitting plate called a light guide plate, and therefore, the number of light sources installed is limited. Therefore, it becomes difficult to brighten the entire display screen as the liquid crystal display device becomes larger, and the role of the optical sheet for improving the brightness becomes important.

As means for improving the brightness of the display screen of the liquid crystal display device, a lens sheet as disclosed in the following Patent Documents 1 to 3 is disclosed, and a representative example thereof is a brightness enhancement film (Brightness Enhancement Film BEF) manufactured by 3M USA. (Registered trademark)) is widely used.
FIG. 14 is a schematic cross-sectional view showing an example in which the BEF 185 is disposed in the liquid crystal display device 180. The liquid crystal display device 180 has a configuration in which a BEF 185 is disposed on the light emission side of the light source 182 and a liquid crystal display panel 184 is disposed on the emission surface side. FIG. 15 is a perspective view of BEF185. The BEF 185 is an optical film in which columnar unit prisms 187 having a triangular cross section are periodically arranged in one direction on a substrate 186. The unit prism 187 has a size (pitch) larger than the wavelength of light.

  The BEF 185 collects light from “off-axis” and redirects this light “on-axis” or “recycle” toward the viewer. can do. That is, the BEF 185 can increase the on-axis luminance by reducing the off-axis luminance when the display is used (observation). Here, “on the axis” means a direction that coincides with the viewing direction F ′ of the viewer, and is generally on the normal direction side with respect to the display screen.

  On the other hand, a light guide plate used in an edge light type liquid crystal display device is generally provided with a light reflecting surface that efficiently guides incident light incident from the end surface to the exit surface, facing the exit surface. Is. The light reflecting surface is for reflecting light that is not directly emitted from the exit surface, out of incident light from the light source, in various directions in the light guide plate and is directed toward the exit surface side. For example, as described in Patent Document 4 and the like, light having various configurations for efficiently leading to the exit surface, such as a printed white dot pattern or a lens shape. Reflective surfaces have been proposed.

  However, no matter what the light reflection surface is, the image of the optical structure such as a white dot pattern or lens shape formed on the light reflection surface is visually recognized as a pseudo light source, and therefore, the problem of uneven brightness is visually recognized. As a means for solving the problem, a method of using a diffusion film as shown in Patent Document 5 is generally used between the light guide plate and the lens sheet.

Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2005-293940 A JP 2004-295080 A

However, the diffusion film used for concealing the image of such an optical structure does not have a light collecting function and has a drawback that the luminance in the front direction is insufficient. In order to obtain sufficient luminance in the front direction, it is necessary to dispose a plurality of lens sheets such as BEF185, but this makes it impossible to reduce the thickness of the display device or increase the manufacturing cost. The problem arises.
In addition, when a means for improving unevenness due to a difference in luminance is configured using only a lens sheet such as BEF185 without using a diffusion film, the above-described optical structure cannot be concealed.
Therefore, the appearance of an optical sheet that conceals an optical structure while having a light collecting function is desired.

  The present invention has been made in order to solve the above-described conventional problems, and conceals an image of an optical structure provided on a reflection surface of a light guide, and improves the luminance in the front direction. An object of the present invention is to provide a lighting unit including the display unit and a display device using the lighting unit.

で表される（１）式の角度ξを用いて、

で表される（２）式の傾き密度分布Ｄ（ξ）と配光分布ｇ（θ）との間に、負の相関があることを特徴とする。
本発明による照明ユニットによれば、光源から射出された光が導光体で反射させられて隠蔽レンズシートに入射して、光出射側に設けた複数の第一の線状レンズによって射出する光を観察者側へ立ち上げることができるため、導光体の反射面に光学構造物が設けられていてもその像を線状に拡散させて隠蔽することができる。
しかも、（１）式で表される角度ξ（傾き角φ（ｘ）に含まれる）を用いて、（２）式で表される傾き密度分布Ｄ（ξ）と配光分布ｇ（θ）との間に負の相関を持たせたことによって、観察者側から観察したときの光学構造物の像について線状に拡散させた隠蔽を均一に行うと共に、複数の線状レンズが配列されているために光を集光させて正面方向の輝度を向上できる。 In order to achieve the above object, the present invention employs the following configuration.
An illumination unit according to the present invention includes a light source, a first emission surface that emits light emitted from the light source and emits the light toward an observer, and at least a part of incident light that faces the first emission surface. A light guide having a reflecting surface on which an optical structure that reflects and guides to the first exit surface is disposed, an incident surface that makes incident light emitted from the exit surface of the light guide incident, and opposite the entrance surface A concealment lens sheet having a second exit surface for uniformizing and emitting incident light, the concealment lens sheet comprising: a light-transmitting base material; A plurality of first linear lenses having a substantially convex curved section arranged in at least one direction on the exit surface side of the first linear lens from the point of contact with the base material of the first linear lens X is the displacement relative to the lens arrangement direction, and the direction perpendicular to the entrance surface of the substrate (or the exit surface of the light guide) The angle between the incident light on the incident surface of the substrate (or the direction of the light emitted from the light guide) is θ, the refractive index of the first linear lens is n, and the extension of the first linear lens The upper frame line forming the outline of the cross section cut by the plane perpendicular to the current direction is f (x), the inclination angle of the tangent line of the upper frame line f (x) is φ (x), and the first light emitted from the light guide When the light distribution with respect to the arrangement direction of one linear lens is g (θ),

Using the angle ξ in the equation (1) expressed by

It is characterized in that there is a negative correlation between the gradient density distribution D (ξ) and the light distribution g (θ) in the equation (2).
According to the illumination unit according to the present invention, the light emitted from the light source is reflected by the light guide, enters the concealment lens sheet, and is emitted by the plurality of first linear lenses provided on the light exit side. Therefore, even if an optical structure is provided on the reflecting surface of the light guide, the image can be diffused in a line and concealed.
In addition, using the angle ξ (included in the inclination angle φ (x)) expressed by the equation (1), the gradient density distribution D (ξ) and the light distribution g (θ) expressed by the equation (2). By having a negative correlation with the image, the image of the optical structure when observed from the observer side is uniformly concealed by linear diffusion, and a plurality of linear lenses are arranged. Therefore, the brightness in the front direction can be improved by condensing light.

で表される（３）式の角度ψを用いて、角度θが０＜θ＜ψを満たす範囲において、傾き密度分布Ｄ（ξ）と配光分布ｇ（θ）が略反比例の関係があることが好ましい。
これによって、配光分布ｇ（θ）の増大に応じて傾き密度分布Ｄ（ξ）を概略で低減させることができる。 In addition, a plurality of optical structures that reflect incident light are regularly arranged in a regular hexagonal arrangement or the like on the reflecting surface of the light guide, and the optical structures with respect to the arrangement direction of the first linear lenses are arranged. When the pitch is p, the thickness of the light guide plate is d, and the refractive index of the light guide plate is m,

The gradient density distribution D (ξ) and the light distribution g (θ) are approximately inversely proportional to each other in the range where the angle θ satisfies 0 <θ <ψ. It is preferable.
As a result, the gradient density distribution D (ξ) can be roughly reduced as the light distribution g (θ) increases.

Further, regarding the gradient density distribution D (ξ), the light distribution distribution g (θ), and the incident angle θ of the incident light on the substrate, the difference between the maximum value and the minimum value of D (ξ) × g (θ) × cos θ is It is preferable that the average value or less.
If this ratio is larger than the average value of D (ξ) × g (θ) × cos θ, a bright region and a dark region can be distinguished, and if it is less than the average value, the image of the optical structure is spread and concealed.

In addition, the direction from an arbitrary optical structure to the second proximity optical structure, which is another optical structure that is second closest to the optical structure, and the arrangement direction of the first linear lenses are substantially the same. It is preferable that
In this case, the pseudo light source, which is an image of the optical structure, spreads in a direction from an arbitrary optical structure to the second adjacent optical structure, and spreads in a direction from the arbitrary optical structure to the nearest optical structure 15. There is no gap between these optical structures because they are close to each other. Therefore, luminance unevenness can be suppressed. On the other hand, the direction from an arbitrary optical structure to the second adjacent optical structure, which is another optical structure that is second closest to the optical structure, and the arrangement direction of the first linear lenses are substantially orthogonal to each other. Then, since the pseudo light source does not spread in the direction from the above-mentioned arbitrary optical structure toward the second proximity optical structure, a large gap is formed and luminance unevenness can be visually recognized.

Moreover, it is preferable to have a plurality of second linear lenses arranged in a direction substantially orthogonal to the arrangement direction of the first linear lenses on the incident surface side of the concealing lens sheet.
In this case, since the first and second linear lenses are arranged substantially orthogonally across the substrate, the light distribution g (θ) with respect to the arrangement direction of the first linear lenses described above also changes greatly. There is no loss of concealment effect. Furthermore, since the second linear lens can expand the pseudo light source in a direction that cannot be expanded by the first linear lens, the concealment effect is further enhanced.

Moreover, it is preferable to further include a reflection sheet that reflects light emitted from the reflection surface side of the light guide and guides it again to the light guide on the opposite side of the light guide from the concealing lens sheet.
Thereby, even if a part of the light emitted from the light source to the light guide leaks to the side opposite to the exit surface, it can be reflected by the reflection sheet in the direction of the concealing lens sheet.

A display device according to the present invention includes any one of the illumination units described above and an image display element that defines a display image.
According to the display device of the present invention, it is possible to observe a high-luminance display image by suppressing uneven brightness in the dark and dark due to the pseudo light source by the illumination unit.

Further, it is preferable that the image display element displays an image by transmission / shielding in pixel units.
If an image is displayed by transmitting / blocking light in pixel units, an image with high image quality can be displayed by using light with reduced luminance unevenness by the illumination unit.

According to the illumination unit and the display device using the concealment lens sheet according to the present invention,
By arranging a concealing lens sheet in which a plurality of first linear lenses are arranged on the light emitting side of the light guide, an optical structure provided on the light reflecting surface of the light guide causes the arrangement of the linear lenses. Since the emitted light can be raised, the image of the optical structure can be concealed linearly.
Moreover, the displacement of the first linear lens with respect to the arrangement direction from the point in contact with the base material is x, the angle between the direction perpendicular to the incident surface of the base material and the direction of incident light on the base material is θ, Where n is the refractive index of the linear lens, f (x) is the upper frame line of the cross section cut by the plane perpendicular to the extending direction of the first linear lens, and the first light emitted from the light guide When the light distribution with respect to the arrangement direction of the linear lenses is g (θ), the gradient density distribution D (ξ) represented by the equation (2) is distributed using the angle ξ represented by the equation (1). By having a negative correlation with the light distribution g (θ), the image of the optical structure when observed from the observer side can be diffused linearly to make the concealment uniform.

Moreover, since the concealment lens sheet has a plurality of linear lenses arranged, it has a condensing function and can obtain higher brightness than the diffusion sheet.
Therefore, according to the illumination unit and the display device using the illumination unit according to the present invention, it is possible to conceal the image of the optical structure provided on the light reflection surface of the light guide and improve the luminance in the front direction.
In addition, according to this display device, it is possible to effectively reduce the luminance unevenness of the display screen and to emit uniform light.

It is principal part sectional drawing which shows an example of the display apparatus by embodiment of this invention in the isolation | separation state. It is a schematic diagram which shows an example of the optical path diagram in a light-guide plate. It is a perspective view of the concealment lens sheet in the illumination unit shown in FIG. It is a figure which shows the upper frame line and its tangent in the cross section orthogonal to the extension direction of a 1st linear lens in the concealment lens sheet | seat shown in FIG. It is explanatory drawing which showed the optical path of the light inject | emitted from the 1st linear lens in a concealment lens sheet. (A) is explanatory drawing which shows the optical path which the pseudo | simulation light source in embodiment spreads through a concealment lens sheet, and the figure which shows the light intensity distribution, (b) is the pseudo | simulation in the case of arrange | positioning a prism sheet instead of a concealment lens sheet. It is explanatory drawing which shows the breadth of the optical path of a light source, and a figure similar to (a) which shows a light intensity distribution map. It is an example of the optical path diagram of the light reflected and emitted by the optical structure in the light guide plate. (A) is a figure of the upper frame line in the longitudinal section of the 1st linear lens of a concealment lens sheet, (b) is an explanatory view showing change of inclination df (x) / dx of a tangent to an upper frame line, (c) ) Is an explanatory diagram showing a change in the gradient density d (x) with respect to the upper frame line. (A) and (b) are intervals of spread of the image of the pseudo light source due to the difference in the arrangement direction of the first linear lenses of the concealment lens sheet with respect to the light reflecting surface of the light guide plate in which the light source structures (pseudo light sources) are arranged in hexagons. It is explanatory drawing which showed the difference. It is a perspective view which shows the modification of the concealment lens sheet which arranged the 2nd linear lens in the light-incidence surface. It is principal part sectional drawing which cut the concealment lens sheet | seat by the modification shown in FIG. 10 with the surface perpendicular | vertical to the extending direction of a 1st linear lens. It is a figure which shows the lens shape of the upper frame line of the 1st linear lens of the concealment lens sheet | seat by an Example. It is a figure which shows the relationship of inclination density distribution D (ξ) with respect to light distribution g ((theta)) in each 1st linear lens shown in FIG. It is a cross-sectional schematic diagram which shows an example of the display apparatus which has arrange | positioned the lens sheet by a prior art. It is a perspective view of the lens sheet shown in FIG.

Below, the illumination unit by embodiment of this invention and the display apparatus provided with this illumination unit are demonstrated. FIGS. 1 to 13 are schematic diagrams, and the size and shape of each part are exaggerated as appropriate for easy understanding.
A display device 1 shown in FIG. 1 includes an image display panel 2 and an illumination unit 3 arranged facing the light incident side of the image display panel 2.
The image display panel 2 arranged closest to the observer side F includes two polarizing plates (polarizing films) 4 and 5 and an image display element 6 sandwiched therebetween. The image display panel 2 is composed of, for example, a liquid crystal display panel. In that case, the image display element 6 is configured by filling a liquid crystal layer between two glass substrates.

The image display panel 2 is preferably an element that displays an image by transmitting / blocking light in pixel units. If an image is displayed by transmitting / blocking light in pixel units, an image with high image quality can be displayed by using light with reduced luminance unevenness by the illumination unit 3.
The liquid crystal display element selected as the image display element 6 is a typical element that transmits and blocks light in pixel units and displays an image, and can improve image quality compared to other display elements. .

The illumination unit 3 is an edge light type illumination device, is disposed facing the light incident side of the image display panel 2, and includes a light source 8, a light guide plate 9, and a concealment lens sheet 10 along the light optical path. It is configured. In addition, a reflective sheet 11 is provided on the back side of the light guide plate 9.
Examples of the light source 8 include a linear light source and a point light source. Examples of the linear light source include fluorescent tubes such as CCFL, HCFL, and EEFL. Examples of the point light source include an LED, and examples of the LED include a white LED and an RGB-LED. Although FIG. 1 shows an example in which the light source 8 is arranged on one end face of the light guide plate 9, the present invention is not limited to this, and the case where the light source 8 is arranged on two opposing end faces, or the case where it is arranged on four end faces. Etc. can also be adopted. At this time, the shape of the light guide plate 9 may be a wedge shape as shown in FIG. 1, or may be a flat plate shape as shown in FIG.

A light reflecting surface 14 is formed on a surface of the light guide plate 9 facing the exit surface 13 disposed on the observer side F. The light reflecting surface 14 is a surface for reflecting light that is not directly emitted from the exit surface 13 out of incident light from the light source 8 in various directions in the light guide plate 8 and is directed toward the exit surface 13 side. The surface 14 is provided with a plurality of optical structures 15 for reflecting incident light (see FIG. 2).
As the optical structure 15, for example, white diffuse reflection dots are printed and arranged. As another example, a structure such as a microlens shape or a prism shape may be formed. As an example, in the light guide plate 9 shown in FIG. 2, a flat plate shape in which white diffuse reflection dot patterns are printed at a predetermined interval is shown as the optical structure 15, and an optical path of light incident from the light source 8 is illustrated. Yes. FIG. 7 shows an optical structure 15 having a microlens shape.

A reflective sheet 11 is provided on the back side of the light guide plate 9, that is, on the side opposite to the concealing lens sheet 10. Therefore, the light emitted from the light reflection plate 14 side opposite to the exit surface 13 from the light guide plate 9 is returned into the light guide plate 9 by the reflection sheet 11 and emitted from the exit surface 13.
In general, since the light guide plate 9 is a transparent plate, the optical structure 15 of the light reflecting surface 14 is visually recognized from the observer side F as a pseudo light source 15 ′. Therefore, in the edge light type illumination unit 3, in order to conceal the light reflection surface 14 on the light guide plate 9, a diffusion film having strong diffusibility is generally used. However, since such a diffusion film has almost no light collecting performance, it is not adopted in the present invention.

  Therefore, in the illumination unit 3 according to the present embodiment, the concealing lens sheet 10 is disposed on the exit surface side of the light guide plate 9 in order to eliminate unevenness in brightness and to collect light. This conceals the pseudo light source 15 ′ by the optical structure 15 on the light reflecting surface 14 of the light guide plate 9, reduces optical unevenness without diffusing the light emitted from the light guide plate 9, and condenses in the front direction. I tried to do it.

  In the concealment lens sheet 10 shown in FIGS. 3 and 4, a flat and light-transmitting base material 17 is provided on the surface facing the light guide plate 9, and the base material 17 has a light emitting direction surface in one direction. A plurality of arranged first linear lenses 18 are arranged. The first linear lens 18 is composed of unit lenses having a substantially convex curved shape in a longitudinal sectional view extending in a bar shape in one direction and a plurality of unit lenses arranged in a direction substantially orthogonal to the extending direction of the unit lenses. Yes. Note that the upper frame line 18a forming the ridge line of the longitudinal sectional shape of the first linear lens 18 is not a convex curve such as a strict semicircle or semi-elliptical shape, and may include, for example, a straight line portion.

Here, in FIG. 4, a cross section taken along a plane perpendicular to the extending direction of the first linear lens 18, where x is the displacement in the arrangement direction from the point of contact of the first linear lens 18 with the base material 17. An upper frame line 18a that is a ridge line of f is assumed to be f (x). In FIG. 5, the angle formed between the direction perpendicular to the incident surface 17a of the concealing lens sheet 10 and the incident direction of the light exiting from the exit surface 13 of the light guide plate 9 to the incident surface 17a is defined as θ. The refractive index of the lens 18 is n, and the light distribution of the incident light from the light guide plate 9 to the concealment lens sheet 10 in the arrangement direction of the first linear lenses 18 is a function g (θ) of the angle θ.
Here, it is assumed that the exit surface 13 of the light guide plate 9 and the entrance surface 17a of the base material 17 of the concealment lens sheet 10 are substantially parallel. Further, the inclination angle of the tangent line 19 of the upper frame line f (x) with respect to the base material 17 is defined as φ (x). Then, the inclination angle φ (x) of the tangent line 19 and the upper frame line f (x) have a relationship as shown in the following expression (4).

  Here, in FIG. 5, the inclination angle φ of the tangent line at which the incident light with the incident angle θ on the concealment lens sheet 10 is emitted almost parallel to the observer side F by the concealment lens sheet 10 is the incident angle θ. Using the refraction angle η, the following expression (5) and expression (6) are given by Snell's law on the incident surface 17 a of the concealing lens sheet 10 and the exit surface from the first linear lens 18.

  When the refraction angle η is eliminated and the inclination angle φ of the tangent line 19 is solved by the equations (5) and (6), the following equation (7) is given. That is, the inclination angle φ of the tangent line that is emitted in parallel to the observer direction F with respect to the incident angle θ is uniquely determined. FIG. 5 shows an optical path of light that enters the base material 17 of the concealing lens sheet 10 from the light guide plate 9 and exits from the first linear lens 18.

As described above, the light emitted from the light source 8 enters the light guide plate 9 and is emitted to the observer side F, but most of the light is a plurality of optical structures 15 arranged on the light reflecting surface 14. Is reflected toward the exit surface 13 side. Therefore, when observed from the observer side F, the optical structure 15 is visually recognized as a pseudo light source 15 ′ as shown in FIGS. 6 and 9.
6 (a) and 6 (b) show the spatial dependence of the path of the light beam emitted from the pseudo light source 15 'and the light intensity when observed from the observer side F. FIG. In addition, the broken line in FIG. 6 shows the spatial dependence of the light intensity when the concealment lens sheet 10 is not arranged.

When the concealment lens sheet 10 is disposed with respect to such a pseudo light source 15 ′ as in the present embodiment shown in FIG. 6A, the pseudo light source 15 ′ is arranged in one direction when observed from the observer direction F. The light from the pseudo light source 15 ′ is diffused over a wide range by the plurality of first linear lenses 18, and the light intensity exhibits a distribution spreading in a gentle convex curve. Therefore, in order to conceal the pseudo light source 15 ′, it is necessary to dispose the concealing lens sheet 10 on the exit surface side of the light guide plate 9.
On the other hand, as shown in FIG. 6B, when the prism lens sheet 12 in which the prisms 12a having only two specific inclinations are arranged on the light emission side of the pseudo light source 15 ′, the observer direction F The spatial spread of the light intensity distribution based on the pseudo light source 15 ′ when observed from the point of view is focused so as to have two sharp peaks. In this case, the pseudo light source 15 ′ is visually recognized as light intensity split into two, and the effect of reducing luminance unevenness is small.

  That is, of the incident light to the concealing lens sheet 10, the intensity g (θ) having an incident angle θ, that is, the light distribution distribution g (θ) and the inclination angle φ of the tangent line 19 of the upper frame line f (x). If there is a negative correlation between the ratio of the angle ξ given by the following equation (1), the inclination ratio of the tangent line 19 that raises the strong incident angle θ in the front direction can be reduced. When observed from the observer direction F, it becomes possible to expand spatially without increasing the difference in brightness. Here, having a negative correlation means that the correlation coefficient becomes negative.

  Further, the proportion of the angle ξ in the inclination angle φ of the tangent line 19 of the upper frame line 18a (f (x)) is proportional to D (ξ) given by the following equation (2). The right side of the equation (2) is the reciprocal of the differential value with respect to the displacement x of the inclination angle φ (x) of the tangent line 19 of the upper frame line 18a, and for example, a certain displacement within the inclination angle φ (x) of the tangent line 19 This is because the inclination angle φ (x1) at x1 is a value proportional to the proportion of ξ. Here, this value is simply defined as the gradient density distribution D (ξ). Note that the gradient density distribution D (ξ) converts the variable from the displacement x to the gradient angle ξ of the tangent line 19. In addition, a variable whose displacement is x is represented as a gradient density d (x).

  Here, when the pitch of the first linear lens 18 is P, the inclination angle φ (x) of the displacement x and the tangent line 19 within the range of 0 <x <P / 2 or P / 2 <x <P. Are uniquely determined from each other. That is, it is assumed that the upper frame line 18a (; f (x)) of the first linear lens 18 decreases monotonously as the displacement x moves away from x = P / 2.

That is, there is a negative correlation between the gradient density distribution D (ξ) expressed by the equation (2) and the light distribution g (θ) using the angle ξ expressed by the equation (1). The image of the optical structure 15 on the light reflecting surface 14 of the light guide plate 9 can be concealed.
The region satisfying this relationship includes at least the central portion of the display device 1 or the illumination unit 3, and preferably includes all regions within the effective range of the display device 1 or the illumination unit 3. Here, the effective range refers to a range in which the illumination unit 3 exhibits a function capable of effectively irradiating illumination light to the outside. For example, the optical path is blocked or the illumination light is hidden by a frame or the like provided around the illumination unit 3. This refers to the irradiation area excluding the area to be applied. The central portion represents a central region when the effective range region is divided into nine.
Hereinafter, unless otherwise specified, the spatial range is the central portion or the effective range region.

The concealment lens sheet 10 not only has a high concealment effect, but also has a light condensing effect because it is a lens sheet. Therefore, it can be used for the purpose of improving luminance. By increasing the gradient density distribution D (φ1) of the gradient angle φ1 having a large light collection effect in a range in which a negative correlation is provided between the gradient density distribution D (ξ) and the light distribution g (θ), It is possible to enhance the brightness improvement effect.
In order to further enhance the concealment effect, it is preferable that the gradient density distribution D (ξ) and the light distribution g (θ) have a substantially inverse relationship. However, it is assumed that the angle ψ represented by the following equation (3) is used and the incident angle θ is in a range satisfying 0 <θ <ψ. Here, “substantially inversely proportional” does not mean that it is strictly proportional to the reciprocal in the mathematical expression, but it means that if one becomes larger, the other becomes almost smoothly smaller. In this case, for example, the gradient density distribution D (ξ) does not necessarily decrease in a single tone with respect to an increase in the light distribution distribution g (θ), but may be in a general tendency to decrease.

  Although the pseudo light source 15 'can be expanded linearly by the first linear lens 18, if the length of this line (image of the pseudo light source 15') is insufficient, the lines do not overlap each other. Concealment will be worse.

Here, it is assumed that a plurality of optical structures 15 are regularly arranged on the light reflecting surface 14 of the light guide plate 9. 7, the pitch of the optical structure 15 with respect to the arrangement direction of the first linear lenses 18 is p, the thickness of the light guide plate 19 is d, and the refractive index of the light guide plate 19 is m. . Then, the angle emitted from the point farthest from the pseudo light source 15 ′ with respect to the arrangement direction of the first linear lenses 18, that is, the midpoint of the adjacent pseudo light source 15 ′ can be solved using Snell's law. The angle is ψ represented by the above equation (3).
Although the light guide plate 9 shown in FIG. 1 has a tapered shape, the taper amount with respect to the pitch p of the optical structure 15 is sufficiently small. Therefore, even if the light guide plate 9 has a tapered shape, the parallel plate shape shown in FIG. As a uniform thickness d substantially equivalent to that of the light guide plate 9, an equivalent calculation result can be obtained.
That is, in the range where the incident angle θ satisfies 0 <θ <ψ, the gradient density distribution D (ξ) and the light distribution g (θ) are approximately inversely proportional, so that the linear spreads of the pseudo light source 15 ′ overlap each other. In this range, high concealment can be achieved without strong contrast.

In order to further enhance the concealment effect, it is desirable that the difference between the maximum value and the minimum value of D (ξ) × g (θ) × cos θ is equal to or less than the average value.
The inventors of the present invention produced first linear lenses 18 having various shapes in which the difference between the maximum value and the minimum value of D (ξ) × g (θ) × cos θ was finely changed in proportion to the average value. As a result of examining how the pseudo light source 15 'is concealed, when this ratio is larger than the average value, bright and dark spots can be visually recognized, and when the ratio is smaller than that, the pseudo light source 15' spreads uniformly. , Confirmed that it was concealed.
Here, cos θ is multiplied by the above formula because when the light emitted from the light guide plate 9 enters the concealment lens sheet 18, the intensity of the incident angle θ is multiplied by cos θ due to the spread due to the incidence. It is in consideration of that. That is, if the incident light intensity in the direction perpendicular to the incident surface 17a (θ = 0 °) is 1, the intensity of incident light having an incident angle θ on the incident surface 17a of the concealing lens sheet 10 as shown in FIG. This is because cos θ. This is because the irradiation area of incident light is 1 / cos θ.

FIG. 8 is a graph showing the relationship between the upper frame line 18 (f (x)) of the first linear lens 18 and the inclination df (x) / dx of the tangent line 19 and the inclination density d (x). Show.
In FIG. 8A, when the lens shape of the substantially convex curved surface of the first linear lens 18 in the concealment lens sheet 10 is shown as the upper frame line 18a (f1 (x1)), the horizontal axis represents the displacement x, and the vertical axis represents the displacement x. f (x) is indicated. Then, the inclination of the upper frame line 18a by one-time differentiation is as shown in FIG. 5B, and the inclination is the largest at both ends of the upper frame line 18a of the convex curved surface and the change is the smallest at the top.

The gradient density d (x) of the upper frame line 18a shown in FIG. 8A is as shown in FIG. In FIG. 8C, the gradient density d (x) gradually increases in the direction of displacement x from the intersection of the upper frame line 18a with the first base material 17 and reaches a maximum value, and then decreases to the upper frame line 18a. The smallest minimum value at the vertex. Thereafter, the gradient density d (x) increases, and a graph having a shape close to a sine curve that reaches the minimum value via the maximum value is obtained.
The graph shown in FIG. 8 is an example, and the present invention is not limited to the shape of the graph shown in FIG.

  The concealing lens sheet 10 is molded on the light transmissive substrate 17 using UV or radiation curable resin, or PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP ( It can be formed by an extrusion molding method, an injection molding method, or a hot press molding method well known in the art using a cycloolefin polymer).

As described above, according to the display device 1 including the illumination unit 3 according to the present embodiment, the first linear lens 18 extending in one direction is substantially orthogonal to the light exit surface 13 side of the light guide plate 9. By disposing the concealment lens sheet 10 arranged in the direction of the light, the light emitted in the arrangement direction of the first linear lenses 18 is diffused by the optical structure 15 provided on the reflection surface 14 of the light guide plate 9. The image of the optical structure 15 can be spread linearly so as to overlap each other and concealed.
Moreover, the displacement of the first linear lens 18 in the arrangement direction of the linear lens 18 from the point in contact with the base material 17 is x, and the direction perpendicular to the incident surface of the base material 17 (the exit surface 13 of the light guide plate 9). The extending direction of the first linear lens 18, where θ is the angle formed by the direction of incident light (emitted light from the light guide plate 9) to the substrate 17, and n is the refractive index of the first linear lens 18. When the upper frame line 18a of the cross section cut by a plane perpendicular to is f (x) and the light distribution with respect to the arrangement direction of the exit surface 13 of the light guide plate 9 is g (θ), it is expressed by the equation (1). Using the angle ξ, observation was performed from the observer side F by providing a negative correlation between the gradient density distribution D (ξ) and the light distribution g (θ) expressed by the equation (2). The linear concealment of the image of the optical structure 15 can be made uniform.

The concealing lens sheet 10 has a condensing function because a plurality of first linear lenses 18 having a substantially convex curve in section are arranged, and a conventional diffusion sheet is used for the light in the F direction on the viewer side. Higher brightness than that obtained can be obtained.
Therefore, according to the illumination unit 3 and the display device 1 using the illumination unit 3 according to the present embodiment, the image of the optical structure 15 on the light reflecting surface 14 of the light guide plate 9 is concealed and the luminance in the front direction is improved. be able to. In addition, luminance unevenness on the display screen can be effectively reduced, and uniform light can be emitted.

In addition, this invention is not limited to embodiment mentioned above, In the range which does not deviate from the meaning, it can change suitably.
For example, in the above description, the shape in which the first linear lenses 18 are arranged in only one side has been described for the sake of simplicity. However, the concealing lens sheet 10 in the present invention is not necessarily arranged or extended in only one direction. It is not necessary to have only the linear lens group 18. For example, as a first modification of the concealment lens sheet 10, a cross lens shape in which the linear lenses 18 are arranged in two directions substantially orthogonal to the exit surface side of the base material 17 may be employed. In this case, the relationship between the light distribution and the lens shape according to the above-described embodiment of the present invention is established for at least one of the first linear lenses 18 and 18 arranged in two directions. Features.

In addition, regarding the arrangement of the concealment lens sheet 18, when a plurality of optical structures 15 are regularly arranged on the light reflection surface 14 of the light guide plate 9, for example, when arranged in a hexagonal manner, any optical structure 15 It is desirable that the direction toward the second proximity optical structure 15 that is second closest to the optical structure 15 and the arrangement direction of the first linear lenses 18 are substantially the same.
In FIG. 9, the optical structure 15 is arranged in, for example, a regular hexagon, and the difference in the spread of the pseudo light source 15 ′ due to the difference in the arrangement direction of the first linear lenses 18 in this case is shown.

  FIG. 9A shows the arrangement direction of the first linear lenses 18 from an arbitrary optical structure 15p (pseudo light source 15p ′) to the nearest optical structure 15q (pseudo) that is closest to the optical structure 15p. The case where it is substantially the same in the direction toward the light source 15q ′) is shown. In this case, the pseudo light source 15 'spreads in the direction from the optical structure 15p (pseudo light source 15p') toward the closest optical structure 15q (pseudo light source 15q '), but the optical structure 15p (pseudo light source 15p'). ) To the second proximity optical structure 15r (pseudo light source 15r ′), a large gap is created.

On the other hand, in FIG. 9B, the second linear optical system in which the arrangement direction of the first linear lenses 18 is second closest to the optical structure 15p from the arbitrary optical structure 15p (pseudo light source 15p ′). The case where it is substantially the same in the direction which goes to the structure 15r (pseudo light source 15r ') is shown. In this case, on the contrary, the pseudo light source 15 'spreads in the direction from the optical structure 15p (pseudo light source 15p') to the second proximity optical structure 15r (pseudo light source 15r '), and is closest to the optical structure 15p. Although it does not spread in the direction toward the object 15q (pseudo light source 15q ′), the optical structures 15p and 15q (pseudo light sources 15p ′ and 15q ′) are close to each other, so that there is no large gap.
Therefore, the arrangement of the concealing lens sheet 10 in the direction shown in FIG. 9B can suppress luminance unevenness with respect to the arrangement of the optical structure 15 on the reflecting surface 14.

Further, as a modification of the illumination unit 3 and the display device 1 according to the embodiment of the present invention, in order to enhance the concealment effect, as shown in FIG. 10 and FIG. The second linear lenses 20 may be arranged in a direction substantially orthogonal to the arrangement direction of the linear lenses 18.
In this case, since the two sets of linear lenses 18 and 20 are substantially orthogonal, the light distribution g (θ) with respect to the arrangement direction of the first linear lenses 18 described above does not change greatly. Therefore, the concealment effect in the above-described embodiment is not lost.
Furthermore, since the second linear lens 20 can expand the pseudo light source 15 ′ in a direction that cannot be expanded by the first linear lens 18, the concealment effect is further enhanced.

  In addition, most of the light incident on the light guide plate 9 is reflected by the light reflecting surface 14 and is emitted from the exit surface 13, so that there is much light with a large angle toward the observer side F. Therefore, the second linear lens 20 is placed on the incident surface 17a side of the base material 17 in a direction substantially orthogonal to the first linear lens 18 so that the emitted light with the inclined angle is raised to the front. You may have. That is, for the purpose of improving the brightness, the second linear lens 20 may be arranged on the incident surface 17a side of the concealing lens sheet 10.

As another modification, an optical sheet including a diffusing element may be additionally arranged on the surface on the viewer side F of the concealing lens sheet 10. By including the diffusing element, the light spread linearly by the concealing lens sheet 10 can be blurred and spread in all directions. Thereby, luminance unevenness can be further reduced.
However, since the luminance unevenness can be reduced by the above-described concealing lens sheet 10, it is not necessary to use a diffusion sheet having strong diffusion characteristics as the optical sheet including the diffusion element. Therefore, the total light transmittance can be increased, and the reduction in luminance due to the optical sheet including this diffusing element can be suppressed.

The lighting unit 3 and the display device 1 including the lighting unit 3 according to the embodiment of the present invention have been described above. However, the lighting unit 3 is not applied only to the display device 1. That is, the illumination unit 3 having a function of efficiently collecting light emitted from the light source 8 can be used for other display devices and illumination devices other than the liquid crystal display device, for example.
Examples of the present invention will be described in detail below, but it goes without saying that the present invention is not limited to the following examples.

  As the illumination unit 3, white LEDs are arranged as light sources 8 on four sides of an acrylic light guide plate 9, and white dot patterns are regularly formed as hexagonal arrangements as optical structures 15 on the reflective surface 14 of the light guide plate 9. Has been. On the viewer side of the light guide plate 9, the illumination unit 3 is configured by sequentially stacking the concealment lens sheet 10 and the diffusion sheet according to the above-described embodiment. Here, each of the illumination units 3 using the four kinds of light guide plates 9 in which the arrangement pitch of the optical structures 15 was 1.4 mm, 2.6 mm, 3.2 mm, and 3.6 mm was prepared.

A polycarbonate resin was used as the material of the concealment lens sheet 10. This is because the polycarbonate resin has a high refractive index of about 1.59, so that the concealing lens sheet 10 with higher light collecting performance can be obtained. As the shape of the upper frame line 18a of the first linear lens 18, six types of lenses having a substantially convex curve shape as shown in FIG. 12 are prepared, and these are designated as lenses 1, 2, 3, 4, 5, 6 respectively. did.
Six types of concealment lens sheets 10 in which the first linear lenses 18 formed with the lenses 1, 2, 3, 4, 5, and 6 shown in FIG. . These six types of concealment lens sheets 10 were respectively attached to the four types of illumination units 3 described above and tested.

FIG. 13 shows a graph with the horizontal axis representing the light distribution distribution g (θ) of light emitted from the light guide plate 9 and the vertical axis representing the gradient density distribution D (ξ).
In FIG. 13, it is the lenses 1 and 2 for the first linear lens 18 that have a characteristic that the gradient density distribution D (ξ) decreases as the light distribution g (θ) increases. In general, it can be said that the same tendency is exhibited.

  Further, the illumination unit 3 described above is used, and the lenses 1, 2, 3, 4, 5, and 6 are used as the concealment lens sheet 10, and the illumination unit 3 on which the concealment lens sheet 10 is mounted is irradiated with illumination light. An observation test was conducted. By visually observing from the observer side F, whether or not the image of the pseudo light source 15 ′ was concealed was visually confirmed as presence / absence of luminance unevenness. Table 1 shows the evaluation results of luminance unevenness.

In addition, regarding the relationship between the gradient density distribution D (ξ) and the light distribution g (θ), the angle θ is presented in the range of 0 <θ <ψ using the angle ψ represented by the equation (3). , D (ξ) × g (θ) × cos θ, the maximum value, the minimum value, and the average value were obtained, respectively, and the ratio between the difference between the maximum value and the minimum value and the average value was calculated. The results are shown in Table 2.
Regarding the calculation of D (ξ) × g (θ) × cos θ, the angle ψ is 16 °, 30 ° when the pitch of the optical structure 15 is 1.4, 2.6, 3.2, 3.6. °, 36 ° and 41 °. With this as the upper limit, the angle θ is 0 <θ <16 °, 0 <θ <30 °, 0 <according to the pitch 1.4, 2.6, 3.2, 3.6 of the optical structure 15 described above. The calculation was performed with θ <36 ° and 0 <θ <41 °. Note that D (ξ) is a value determined by the shape of the lenses 1, 2, 3, 4, 5, 6 and the angle θ.

In Table 1 showing the evaluation results of the luminance unevenness, the case where the luminance unevenness could not be observed by visual observation was indicated as ◯, and the case where the luminance unevenness could be observed was indicated as ×.
In the range of the total light distribution g (θ), the lenses 1 and 2 having a substantially inversely proportional relationship in which the gradient density distribution D (ξ) decreases as the light distribution distribution g (θ) increases are described in the examples. Under the conditions shown, no luminance unevenness was observed. In addition, no luminance unevenness was observed under the same conditions for the lens 3 having a substantially inverse relationship.
On the other hand, when the light distribution distribution g (θ) is less than a certain value, for the lenses 4 and 5 that are not substantially inversely proportional, if the pitch of the optical structure 15 is set large, the concealability is insufficient and luminance unevenness is observed. It was done. On the other hand, with respect to the lens 6 in which the gradient density distribution D (ξ) and the light distribution distribution g (θ) do not have a substantially inverse relationship, luminance unevenness was observed even if the pitch of the optical structure 15 was made fine.

  In Table 2, in the case of the concealment lens sheet 10 of lenses 1, 2, and 3, the difference between the maximum value and the minimum value was less than the average value regardless of the arrangement pitch of the optical structures 15. Therefore, the pseudo light source 15 'can be concealed. On the other hand, in the case of the concealment lens sheet 10 of the lenses 4, 5, 6, the average value is generally exceeded, and the pseudo light source cannot be concealed.

From the test results described above, the shape of the first linear lens 18 in the concealment lens sheet 10 has a characteristic that the gradient density distribution D (ξ) decreases as the light distribution distribution g (θ) increases, and the optical As shown in Table 1, even if the arrangement pitch of the structures 15 is changed in the range of 1.4 to 3.6 mm, the pseudo light source 15 ′ of the optical structure 15 can be concealed, and the luminance unevenness can be reduced to an invisible level. .
In the lens shape of the first linear lens 18 having a characteristic that the gradient density distribution D (ξ) decreases with an increase in the light distribution g (θ) at a certain angle or more, the optical structure 15 When the arrangement pitch was small, it was possible to reduce the luminance unevenness to such an extent that it could not be visually recognized.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Image display panel 3 Illumination unit 8 Light source 9 Light guide plate 13 Outgoing surface 14 Reflecting surface 15 Optical structure 15 Pseudo light source 10 Concealed lens sheet 17 Base material 17a Incident surface 18 First linear lens 18a Upper frame line 19 Tangent 20 Second linear lens

Claims (8)

A light source;
A first emission surface that emits light emitted from the light source and emits the light toward an observer; and the first emission surface that faces the first emission surface and reflects at least part of the incident light. A light guide having a reflective surface on which an optical structure leading to
Illumination comprising: a concealing lens sheet having an incident surface on which incident light that exits from an exit surface of the light guide is incident; and a second exit surface that is opposed to the incident surface and emits the incident light after being uniformed A unit,
The concealing lens sheet includes a light-transmitting base material and a plurality of first linear lenses having a substantially convex curved section arranged in at least one direction on the second exit surface side of the base material. Have
The displacement of the first linear lens with respect to the arrangement direction of the first linear lens from the point of contact with the substrate is x, the direction perpendicular to the incident surface of the substrate and the incident light on the substrate An angle formed with the direction is θ, a refractive index of the first linear lens is n, and an upper frame line that forms an outline of a cross section taken along a plane perpendicular to the extending direction of the first linear lens is f. (X), the inclination angle of the tangent to the upper frame line f (x) is φ (x), and the light distribution of the light emitted from the light guide with respect to the arrangement direction of the first linear lenses is g (θ )

Using the angle ξ in the equation (1) expressed by

An illumination unit characterized in that there is a negative correlation between the gradient density distribution D (ξ) of the equation (2) expressed by the above and the light distribution g (θ). A plurality of the optical structures that reflect incident light are regularly arranged on the reflection surface of the light guide, and the pitch of the optical structures with respect to the arrangement direction of the first linear lenses is p, When the thickness of the light guide plate is d and the refractive index of the light guide plate is m,

Using the angle ψ in equation (3) expressed by
2. The gradient density distribution D (ξ) and the light distribution g (θ) have a substantially inversely proportional relationship in a range where the angle θ satisfies 0 <θ <ψ. Lighting unit. Regarding the gradient density distribution D (ξ), the light distribution g (θ), and the angle θ,
3. The lighting unit according to claim 1, wherein a difference between a maximum value and a minimum value of D (ξ) × g (θ) × cos θ is equal to or less than an average value thereof.   The direction from the arbitrary optical structure toward the second proximity optical structure, which is another optical structure that is second closest to the optical structure, and the arrangement direction of the first linear lenses are substantially the same. The lighting unit according to claim 1, wherein the lighting unit is a lighting unit.   The plurality of second linear lenses arranged in a direction substantially orthogonal to the arrangement direction of the first linear lenses are provided on the incident surface side of the concealing lens sheet. Item 5. The lighting unit according to any one of Items 1 to 4.   The light guide is further provided with a reflection sheet that reflects light emitted from the reflection surface side of the light guide and guides it again to the light guide on a side opposite to the concealment lens sheet of the light guide. The lighting unit described in any one of 1 to 5. The lighting unit according to any one of claims 1 to 6,
An image display element for defining a display image;
A display device comprising:   The display device according to claim 7, wherein the image display element displays an image by transmission / shielding in pixel units.

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